1. Field of the Invention
The present invention relates to a steering linkage structure of a rear wheel steering device. More particularly, the present invention relates to a steering linkage structure of a rear wheel steering device which can increase bending strength and reduce the lead diameter and the capacity of a driving motor.
2. Description of Related Art
In general, rear wheel steering devices of vehicles, devices for controlling the direction of the rear wheels of vehicle in accordance with the driving situations of the vehicles, reduces the turning radius of a vehicle by controlling the direction of the rear wheels opposite to the direction of front wheels when the vehicle is driven at a low speed, and improves driving stability by controlling the rear wheel in the same direction as the front wheel when the vehicle is driven at a high speed.
FIG. 1 shows an example of a rear wheel steering device according to the related art. The rear wheel steering device includes driving motor 100 in a housing, a screw nut 110 rotated by power from the driving motor 100, a steering shaft 120 reciprocated to the left and right by the rotation of the screw nut 110, and a linkage 140 coupled to both ends of the steering shaft 120 through ball joints 130, connected with rear wheels (not shown), and controlling the direction of the rear wheels.
A lead 125 is formed on the steering shaft 120 for engagement with the screw nut 110.
In the rear wheel steering device having the structure of the related art, however, the diameter of the steering shaft 120 is set in consideration of a bending load inputted through the linkage 140 and the lead 125 diameter needs to be set larger than the diameter of the steering shaft 120 in consideration of engagement between the lead 125 and the screw nut 110.
Accordingly, since the lead diameter is set large in consideration of the bending load, it is required to increase the output of the driving motor 100 with the increase in the lead diameter, which increases the weight and the manufacturing cost.
As another example of rear wheel steering devices according to the related art for solving the problems, a steering shaft is divided into two, left and right steering shafts, in which the lead diameter of any one of the steering shafts is set as small as possible and the two steering shafts are engaged with a diameter smaller than the lead diameter.
In the different type of rear wheel steering device of the related art, since the steering shaft with the lead is combined with a screw nut and then the other one is bolted to the steering shaft, the assembly ability is improved.
However, since the diameter of the coupling portion of the left and right steering shafts is smaller than the lead diameter, it is weak to buckling due to the axial load in the steering shafts.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.